Samples For all antibiotic assays, 5-10mls blood into red-topped tube (no anticoagulant) DO NOT sample from the line through which the antibiotic has been given.
| Antibiotic | Sampling Time | First Sample | Expected Levels | Usual interval to re-assay
|
| VANCOMYCIN
| Pre-dose only (i.e. within 15 mins before dose)
| Around 2nd – 4th dose | 5 – 15mg/L | 3 days
|
| GENTAMICIN / TOBRAMYCIN (b.d or t.d.s regime) | Pre-dose (within 15 mins before dose) and Post-dose (1hr after dose) | Around 2nd – 4th dose | Pre less than 2mg/L Post 5 – 10 mg/L | 3 days |
| GENTAMICIN / TOBRAMYCIN (once – daily regime) | Post-dose only taken between 6 and 14 hours after dose. N.B. Times of dosing and sampling must be given on request form. | 1st to 3rd dose | Interpretation by Microbiologist | 3 days |
Important Notes
- After taking pre-dose levels, give the prescribed dose as normal – DO NOT wait for the results of the assay.
- “Random” levels should seldom be needed and should only be taken by prior arrangement with the Duty Microbiologist.
- For patients with stable renal function, whose results are within the expected range, assays do not need to be performed more than twice a week. Where renal function is unstable or poor, assays should be discussed with the Duty Microbiologist.

